1911 Encyclopædia Britannica/Rock

ROCK (O. Fr. roke, Sp. roca, Ital. rocca; possibly from a Lat. form rupica, from rupes, rock), in geology a mass of the mineral matter of which the crust of the earth is composed (see Petrology and Geology). In more general usage a “ rock ” is a large mass of this mineral matter, as distinguished from smaller pieces which are termed “ stones.”

From this word must be distinguished the verb “ to rock,” to swing an object to and fro, particularly of a cradle in which a child is rocked to sleep, the original meaning. The O.Eng. word is roccian, and is cognate with many words in Teutonic languages, e.g. Du. rukkea, Dan. rykke, Ger. rücken, to pull, tug, push.